Brillouin spectra of Langmuir-Blodgett films

The Brillouin spectra of thin films of cadmium arachidate have been measured. These films are multiple layers of ordered monolayers (26.8 Å thick) of the cadmium salt of arachidic acid deposited one monolayer at a time onto aluminum and glass substrates by the Langmuir-Blodgett technique.1 The elastic properties of these films can be determined from these Brillouin scattering spectra. Light from a single-mode argon-ion laser at 0.5145 m was scattered by multiple, high frequency, surface acoustic waves guided by LB films of thickness 100, 35, and 11 monolayers. The scattered light was collected and spectrum analyzed with a 9-pass tandem Fabry-Perot interferometer to obtain the velocities of the surface acoustic waves. The use of the tandem interferometer provided the high contrast needed to detect the weak Brillouin signals in the presence of the intense elastically scattered light. The Brillouin spectra are now being analyzed to determine the elastic properties of the Langmuir-Blodgett films.